In the manufacture of electric motors, a basic requirement for high efficiency and low noise is that the air gap between the rotor and stator be maintained within predetermined limits. However, assembly methods for motors often are such that the tolerances do not assure a precise final construction of the motor.
Further in certain types of motors such as used for ceiling fans, it is required to have a conduit extending through the rotating shaft of the motor in order that wiring may be provided to controls and light fixtures suspended from the motor.
Accordingly, among the objectives of the present invention are to provide an electric motor and a method of making and assembling the motor wherein the accumulation of tolerances which would detract from the efficiency and would produce noise are minimized; wherein the motor has a minimum number of parts and can be utilized for ceiling fan operations which require a hollow conduit through which wires may be provided.
In accordance with the invention, the electric motor comprises a lower housing assembly and an upper housing assembly. The lower housing comprises a hollow stationary shaft, a bottom plate mounted on the shaft and a stator mounted on the bottom plate. The upper housing comprises a tube and an integral top plate and a rotor mounted on the plate. The tube of the upper housing assembly is telescoped over the shaft of the lower housing assembly and bearings between the tube and shaft rotatably support the rotor about the stator.
The method of assembling an electric motor comprises forming an upper housing assembly by first forming a generally cylindrical shell, forming an end plate with an axial tube, mounting the end plate on said cylindrical shell with the tube extending axially inwardly, locating the shell radially in an accurate position with respect to the axis of the shell, fastening the end member to the shell to form an upper housing assembly, mounting a radial wall on a hollow shaft, accurately locating a stator on the radial wall in accurate concentric relationship between the stator and the outer diameter of the shaft, fixing the stator in this accurate position to form a lower housing assembly, telescoping the upper housing assembly over the shaft of said lower housing assembly and interposing bearings between the shaft and the tube so that the rotor is in accurate concentric relationship with the stator.